THE RELATIONSHIP BETWEEN CHLOROPHYLL AND THE CAROTENOIDS IN THE ALGAL FLAGELLATE, EUGLENA* BY J. J. WOLKEN AND A. D. MELLON

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1 THE RELATIONSHIP BETWEEN CHLOROPHYLL AND THE CAROTENOIDS IN THE ALGAL FLAGELLATE, EUGLENA* BY J. J. WOLKEN AND A. D. MELLON (From Biophysical Research, Laboratory of Molecular Biology, Eye and Ear Hospital and the University of Pittsburgh School of Medicine, Pittsburgh) (Received for publication, October 20, 1955) Research for the "precursor" of chlorophyll in higher plants stimulated us to search for the "precursor" in Protista using similar techniques. Recently we have obtained an action spectrum for chlorophyll formation in Euglena (1). The action spectrum corresponds with the action spectrum for "greening" in etiolated Arena seedlings as determined by Frank (2) and with the absorption spectrum for protochlorophyll as given by Noack and Kiessling (3 a, b) and Koski and Smith (4). Studies by Smith (5) and Koski and Smith (4) indicate that protochlorophyll is the chlorophyll precursor as indicated in the action spectrum given by Frank (2). While the chlorophyll and carotenoid densities were being followed during this work, a decrease in carotenoid density was observed at high light intensities. Earlier, Strain (6) had suggested that the carotenoids are involved in chlorophyll formation based on the reports that the spectral bands which are most effective in chlorophyll formation are relatively ineffective in carotenoid formation (7) since a temporary depression of carotenoids but a steady increase of chlorophyll had been noted in the leaves of Phaseolus multiflorus on prolonged light exposure (7, 8). Granick has reported a significant decrease in carotenoid density as Mg vinyl pheoporphyrin is transformed to chlorophyll in a mutant of Chlordla (9). A similar decrease in carotenoid density in oat seedlings has been observed at high light intensities and it has been suggested that the substance responsible for the carotenoid decrease is a prophyrin-type compound concerued with "esterifying" the porphyrin molecule and converting Mg vinyl pheoporphyrin to protochlorophyll, its phytol ester (10). In the present paper, an improved action spectrum is presented and, in addition, data on carotenoid formation and "destruction" are given. Also, * This work was supported in part by grants from the United States Public Heath Service, Institute of Neurological Diseases and Blindness (B-397 C), the American Cancer Society (CP-69) on the recommendation of the Committee on Growth, National Research Council, and the National Council to Combat Blindness, Inc. Os8-c). 675 J. Gz~. PI~SXOL., 1956, Vol. 39, No. 5 The Journal of General Physiology

2 676 CHLOROPHYLL AND CAROTENOIDS IN EUGLENA the possible relationships between the two plastid pigments (chlorophyll and carotenoids) in Euglena are explored. Methods E. gracilis vat. bacizlaris was grown in a chemically defined medium (11), in a temperature-controlled room (25 C. =i= 2 ). The organisms were cultured in 100 ml. cotton-stoppered Petroff flasks containing 50 ml. of medium. The use of the small flat flasks results in an even light distribution throughout each culture. The flasks were placed in filter boxes as previously described (1) and exposed to light of different intensities and wave lengths. The light source was a 20 W G.E. fluorescent tube. TABLE I The Reciprocal of Rdali~ Energy for a Constant Amount of Chlorophyll Formed after 96 Hours Exposure to Light of Di~erenl Wave Len tt~ F flter combinations Dominant wave length Relative energy Lo~ relat;ve energy Chlorophyll formation Lo~ Relative energy Relative energy -~.SO l per cent per cent chloro- chlorophyll phyll Coming }- Klett purple Coming }- Wratten purple Coming { Klett blue Coming Klett -k Wratten green Coming Coming Coming Coming Coming Coming m/.t O O per ~ The intensity of the light varied from 50 to 100 foot-candles depending on the distance of the cultures from the lamp. The filters used to vary wave length were Klett, Wratten gelatin, and Coming glass color filters (Table I). Energy distribution curves for the various combinations were obtained using a Beckman DK recording spectrophotometer. By substituting the fluorescent tube for the tungsten lamp on the spectrophotometer, energy distribution recordings could be obtained for the filters in terms of the fluorescent lamp output (Fig. i). The center of gravity of each curve was determined; the wave length corresponding to the center of gravity was taken as the dominant wave length of the filter combination. The relative energy of the filter as Listed in Table I, is the product of the relative energy at the dominant wave length of the filter and the inverse of the square of the distance in centimeters of the culture from the light source.

3 ~'. ~'. WOLKEN AND A. D. MELLON 677 Pigment extractions were done in the following manner. 10 ml. aliquots were taken from the cultures, centrifuged, and the pelleted organisms extracted in 85 per cent aqueous acetone. The extracts were centrifuged until dear and the acetone-pigment solution brought up to a constant volume of 4 ml. All pigment density measurements were made on the Beckman DU spectrophotometer. The density at 663 nag was taken as a measure of chlorophyu concentration and the density at 475 mtt was taken as a measure of carotenoid concentration. All sampling and extractions were done in green light from a Wratten safelight, series OA. 5o f /\ 30L! x [ /\ / ;% ~o 2ol- / \,!'~ I, i 700 m/j FIo. I. Energy distribution of various filter combinations. Arrow denotes dominant wave length. Dotted curves reduced to one-half their height. Curves recorded on Beckman DK recording spectrophotometer. Experimentat Data and Results I. The Action Spectrum ]or Chlorophyll Formation In evaluating the relative effectiveness of various regions of the spectrum for chlorophyll formation, the method of treating the data is essentially that of Frank (2). In a previous study, we have shown that chlorophyll synthesis versus energy at two different wave lengths yields parallel curves (1). This information makes it unnecessary to chart complete chlorophyll formation curves at various relative energies for each wave length; since these two wave lengths yield parauel curves, it is fair to assume that all wave lengths wiu give paralld chlorophyll formation. By placing the data for the two parallel curves on one graph, as well as single experimental points, one can slide one of the paralld curves along the abscissa until it superimposes on the experimental point. One can then read from this curve the log relative energy required to produce a constant amount (50 per cent) of chlorophyll. The reciprocal of this energy plotted against the wave length is the action or effectiveness spectrum for chlorophyu formation. The culture which produced the largest amount of chorophyll was arbitrar-

4 678 CHLOROPHYLL AND CAROTENOIDS IN EUGLEIqA ily selected as 100 per cent chlorophyll formation, and all other cultures were calculated as percentages of this. Table I lists the reciprocals of the relative energy needed for 50 per cent chlorophyll formation at various wave lengths } e, l "~ W m ,, i I ~ I!! ~ I I I I m# FIG. 2. Action spectrum for chlorophyll synthesis in Euglena gracilis. TABLE II Chlorophyll and Carotenoid Formation in Dark-Adapted Euglona gracllis after 96 Hours' Exposure to White Light of Different Intensities Log relative energy Chlorophyll density Csrotenold density 663 m/~ 475 m/~ From this data an action spectrum can be plotted to which two corrections can be made: (1) Not all light transmitted by any filter is effective in chlorophyll formation. By multiplying the energy of the filter and the relative energy from the action spectrum at appropriate wave lengths, new energy distribution curves and new dominant wave lengths can be obtained for each filter combination. (2) A correction for the number of incident quanta should

5 J. ]. WOLKEN AND A. D. MELLON 679 be made by multiplying the reciprocal of the energy from the action spectrum by the energy of the quanta at that wave length. The resultant curve is given in Fig. 2. It will be noted that absorbtion in the blue is lower than in the red. This would indicate that some pigments, probably the carotenoids which absorb strongly in the blue range, are screening the chlorophyll molecules. This has been demonstrated in albino and normal corn leaves by Koski, French, and 0.08 i i ~ 1 I I! i I I o ///" 0.06 I- SS S s S A- Carotenoid Densityl4?5mpl ~,~" 0.05 "~ ~ 0, o i I ~ I i I I i,i I IO Log Relative Energy FIG. 3. The effect of increasing intensity of white light on chlorophyll-carotenoid formation in F.ug/ena. The dotted extension on the carotenoid curve represents expected carotenoid formation in white light if no destruction had taken place. Smith (12). In albino leaves, in which only traces of carotenoids are present, a high blue absorption band is found but in normal leaves, in which carotenoids are in abundance, the absorption in the blue by chlorophyll is lower than in the red. II. Chlorophyll-Carot~wid Formatio, in Light of Varied In~,~siIy Chlorophyll concentration increases with the light intensity for a 96 hour exposure. However, carotenoid concentration increases at first and then decreases as the light intensity is increased. The data are given in Table II and plotted in Fig. 3.

6 680 CHLOROPHYLL AND CAROTENOIDS IN EUGLENA A small amount of pigment persists in darkness but it has been suggested that this is due to chloroplast remnants remaining in dark-adapted organisms (13). The data in Table n have been corrected for this dark-accumulated pigment. TABLE III The Effectiveness of Various Wa~e Lengths in Chlorophyll Formation and in Carotenoid Net Loss over the Expected Gain in White Lo S relative ~ne:r~ DoIiRinant w~ve length "C",, C~ A("C". - Ca) C/~ C/x A(C&o - Clx) I A (Cl~- CI I O O O m# O , Ca = carotenoid density at wave length X, "C'" -- carotenoid density expected at equal intensity of white light, CZa -- chlorophyll density at wave length X, C/~ - chlorophyll density at equal intensity of white light, I,- effectiveness in chlorophyll synthesis, A(C_A, -- CZx) 1 -- effectiveness in carotenoid synthesis, A("C'~, -- Cx) & --- effectiveness in carotenoid loss, A("C"w -- Ca) = measure of net effectiveness of the two processes 1 Lx+ A("c"~ - ca) IlL Effectiveness of Wave Length in Carotenoid Net Loss and Chlorophyll Gain Curves related to the action spectra of carotenoid net loss and chlorophyll synthesis can be reconstructed from these data, using the methods of Frank (10). The greater the amount of pigment formed at a particular wave length, the greater must be its efficiency. Therefore, by subtracting the density of the pigment formed at one wave length, from the density of the pigment formed in an equal intensity of white light, a value will be obtained the re-

7 J. J. WOLY~N AND A. D. MELLON 681 ciprocal of which will be a measure of the effectiveness of that wave length. This is arrived at by reasoning that the greater the efficiency of the particular wave length, the smaller will be the difference between the amount of pigment formed at that wave length and the amount formed in white light. Thus the reciprocal of the difference will be a measure of its effectiveness. Similar reasoning is applied to the amount of carotenoid formation. The difference between the amount of carotenoid expected to be formed (dotted ~ OD20!,<1 O.Ole 0, i I I J I I I, t, i i i i i i i i i m# FIO. 4. Reconstructed curve related to the action spectrum of the substance responsible for carotenoid net removal. curve in Fig. 3) in white light and the amount actually formed at a particular wave length is a direct measure of the effectiveness of that wave length in carotenoid net removal. The data are recorded in Table HI and plotted in Figs. 4 and 5. One must decide what the curve showing effectiveness in carotenoid net removal (Fig. 4) represents: (1) If the same substance is responsible for carotenoid loss and gain, and both are represented in the curve equally, then their spectral properties should cancel each other. (2) If, however, the two substances are widely different and enter into the curve equally, the resultant

8 682 CHLOROPHYLL AND CAROTEN01DS IN EUGLENA curve should be meaningless. Neither of these seems to be the case. (3) If the curve represents mainly the substance concerned with carotenoid removal, the curve itself should suggest the compound responsible; but, the curve does not suggest any known compound. (4) However, if the curve represents primarily the substances responsible for carotenoid synthesis, then the reciprocal of the curve should give the spectral characteristics of that compound. The reciprocal curve of Fig. 4 is plotted in Fig. 5 along with the curve for chloro r~.... r~ Carotenoid o o Chlorophyll I? I ,. -Id i 0 I! I I I I I I! I! I. I 4O rn,u FIG. 5. Reconstructed curves related to the action spectra of the substances responsible for chlorophyll and carotenoid synthesis. The left scale is used with the carotenoid curve and the right scale with the chlorophyll curve. phyll formation. It will be observed that the "fit" of the two curves is very close and for this reason the fourth assumption appears most plausible. DISCUSSION One must decide whether the similarity between the carotenoid synthesis and chlorophyll synthesis curves is meaningful. First the action spectrum for the chlorophyll "precursor" should be considered. Previously, we have suggested from the similarity between our action spectrum and the absorption spectrum of protochlorophyll (1), that the precursor in t~,glemt might be protochlorophyll. However, repeated attempts to identify this pigment both by extraction methods (12) and by fluorescence studies with dark-adapted 40

9 ~. ~'. WOLKEN AND A. D. MELLON 683 organisms have met with failure. A substance fluorescing in the range between 520 to 580 nap has been found in the in vivo dark-adapted organisms, but the substance responsible has not been isolated or identified as yet. No fluorescence was observed in the spectral range of protochlorophyll E O O.2 ~ SO m/j FIG. 6. Absorption spectrum of mixed porphyrins extracted from both dark-adapted Eugl~na and the chlorophyll-free mutant of Eugle'na. E. signifies relative extinction. The scale on the left is five times that on the right. These negative results could indicate that protochlorophyll may not be the chlorophyll precursor in 2Euglena. There is every indication that the precursor is a porphyrin type compound; the wave length of the absorption bands and the peak ratios of the action spectrum indicate this quite strongly. In addition, mixed etioporphyrins have been extracted from dark-adapted organisms (Fig. 6) using a Granick method (14) but it has not been possible to identify any individual porphyrins involved as yet. It may be that the conversion of the "precursor" to chlorophyll is so rapid in Euglena, that the precursor is not built up in suflficient quantity to permit its identification in

10 684 CHLOROPHYLL AND CAROTEI~OIDS IN EUGLENA the normal organisms. In the absence of isolation, the action spectrum must serve as the most reliable indication of the "precursor," and the action spectrum resembles the absorption spectrum of protochlorophyll more than any other known compound of this type. We may again consider the two "action" spectra for chlorophyll and carotenoid synthesis. Frank has reported that carotenoids decrease at high intensities of both red and blue light indicating that the light synthesis of carotenoids is probably not autocatalytic but is influenced by a pigment which absorbs light in both the red and blue portions of the spectra (10). Our "action" spectra for carotenoid synthesis (Fig. 5) seems to substantiate this finding. We have observed the phenomenon of the carotenoid light "destruction" in a chlorophyll-less mutant of Eugl~a which we have recently isolated from our cultures. The mutant, when grown in white light (,~300 foot-candles), produces large quantities of carotenoids for the first 2 weeks. The color of the culture then fades over the period of a week from a brilliant orange to a yellowish brown. Using a method of Granick (14), a pale pink pigment was extracted from 10 gin. of the packed organisms. The absorption spectrum was the same as that obtained with the normal dark-adapted organisms (Fig. 6) again indicating the presence of porphyrins. In addition to the peaks shown, a peak was found at 320 to 330 m~ and another at 230 m/~ in the ultraviolet. However, the pigments were present in very low concentration and no extensive isolation and identification studies could be made. The curve representing the action spectrum for carotenoid net removal (Fig. 4) is extrapolated in both the blue and red regions of the spectra. The shape of the curve seems to indicate that there might be two other absorption bands, one somewhere in the red and one in the near ultraviolet. Frank has suggested that there may be a porphyrin-like system involved in removing carotenoids and subsequently phytolizing the precursor before its conversion to chlorophyll (10). We have found no evidence of the "phytolization." However, the great decrease in carotenoid concentration in the chlorophyll-free mutant, accompanied by a rise in porphyrin concentration, would seem to indicate that the two processes of chlorophyll and carotenoid synthesis are closely related. Also, the close packing of the chlorophyll and carotenoids in the pigment monolayers in the chloroplast would permit interaction or energy transfer among the plastid pigments (15-17). The dose correspondence between the shapes of the "action" spectra of chlorophyll and carotenoid synthesis may be indicative that a similar porphyrin-like molecule influences both chlorophyll and carotenoid synthesis. SUMMARY 1. We have obtained an action spectrum for chlorophyll formation in Eugloria gracili~. This action spectrum is similar to the absorption spectrum of

11 ]'. J. WOLKEN AND A. D. MELLON 685 protochlorophyu. However, efforts to isolate and identify this pigment have been unsuccessful. 2. Porphyrins have been extracted from both the normal and dark-adapted gugl~ and a chlorophyll-free mutant. 3. The "action" spectra for chlorophyll and carotenoid synthesis have been found to almost coincide, indicating that the same porphyrin-like molecule may influence the synthesis of both pigments. 4. It is indicated that two porphyrin-like systems are in operation simultaneously, one concerned with carotenoid "removal" and another involved in carotenoid and chlorophyll synthesis. REFERENCES 1. Wolken, J. J., Mellon, A. D., and Greenblatt, C. L., J. Protozool., 1955, 2, Frank, S. R., J. Gen. Physiol., 1946, 29, (a) Noack, K., and Kiessling, W., Z. physiol. Chem., 1929, 182, 13; (b) 1930, 193, Koski, V., and Smith, J. H. C., J. Am. Chem. Soc., 1948, 70, Smith, J. H. C., Arch. Biochem., 1948, 19, Strain, H., Carnegie Imti~ion of W~hington, Pub. No. 490, Rudolph, H., Pla~a, 1933, 21, Seybold, A., and Egle, K., Pla~a, 1938, 28, Graniek, S., J. Biol. Chem., 1950, 183, Frank, S. R., Arch. Bioc~., 1951, 30, Hutner, S. H., Provasoli, L., Schatz, A., and Haskins, C. P., Proc. Am. Phil. Sot., 1950, 94, Koski, V., French, C. S., and Smith, J. H. C., Arch. Bioch~. and Biophysic., 1951, 31, Wolken, J. J., and Palade, G. E., Ann. New Y~k Aca& Sc., 1953, 56, Graniek, S., J. Biol. Chem., 1948,175, Wolken, J. J., and Schwertz, F. A., J. G~. Physiol., 1953, 37, Arnold, W., and Oppenheimer, J. R., J. Gen. Physiol., 1950, 93, Duysens, L. M. N., Transfer of Excitation Energy in Photosynthesis, Utigeverij-- Maatshappij v/h Kemink en Zoon, N.V. Utrecht, 1952.